Synthesis and spectroscopic analysis of an extended series of hetero dinuclear complexes containing two different lanthanides in 1:1 stoichiometry

An extended series of air and moisture stable and thermally volatile hetero dinuclear complexes of general composition [Ln(1)Ln(2)(fod)(6)(mu-bpm)] (where Ln(1)-Ln(2) = Pr-Nd (1); Nd-Sm (2); Dy-Ho (3); Ho-Er (4); Er-Tm (5); Tm-Yb (6); Yb-Lu (7) and Eu-Tb (8); fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate; bpm = 2,2'-bipyrimidine) have been synthesized and characterised. To explore the stoichiometry of the two different lanthanides in these complexes, we performed a thorough analysis of the f-f absorption spectra of the complexes in solution and found that the hetero dinuclear complexes contain two different lanthanides in 1:1 stoichiometric ratio. Furthermore, the complexes display intense f-f hypersensitive transitions as compared to Ln(3+) aqua-ions. In pyridine (a strong coordinating solvent) the oscillator strength and band shape of the f-f hypersensitive transitions show distinct variations as compared to the oscillator strength and band shape in chloroform (non-coordinating solvent). We attribute this change to a change in asymmetry of the field around Ln(3+) ion due to the coordination of the solvent (pyridine). A thorough investigation of the steady-state emission and excitation spectra of the complexes 3 and 8 in chloroform and pyridine further establishes that pyridine competes for coordination with weak bpm bridge and eventually replaces it to generate two different species in solution,i. e. [Ln(1)(fod)(3)(py)(n)] and [Ln(2)(fod)(3)(py)(n)] (where py = pyridine). (C) 2012 Elsevier B. V. All rights reserved.